1. Field of the Invention
This invention relates to the casting of metal articles. More particularly, it relates to the casting of metal articles in which molten metal is poured into a mould cavity formed in particulate material by destroying a pattern in situ.
2. Description of the Prior Art
One well known example of such a casting method comprises embedding a pattern of foam plastics material, e.g. expanded polystyrene, in binder-free foundry sand, consolidating the sand to form a mould, pouring molten metal into the mould to destroy the pattern by burning or vaporising the pattern so that the metal replaces the pattern and an article corresponding to the original shape of the pattern is cast in the mould cavity previously occupied by the pattern.
Such a method has a number of advantages which include:
1. the ability to produce castings without joint lines and thus with reduced flash thereby requiring less fettling than with conventional moulds comprising cope and drag parts;
2. the process is relatively easy to automate since moulding involves simple filling of particulate material around the pattern using dry binder-free particulate material such as foundry sand;
3. knock-out and de-coring are easy since the unbonded particulate material simply runs off and out of the casting.
However, it suffers from the disadvantage of sporadic filling defects which are unacceptable in castings which are safety critical, such as suspension and steering components for automobiles.